Papers by Keyword: Uniaxial Stress

Abstract: Effects of uniaxial stress, temperatures and electron irradiation on nanochain straightening in film polymer materials (polytetrafluoroethylene and lavsan) have been studied comprehensively. Essential change in material behavior including chain straightening was found in strain (e) – stress (s) curves.

Abstract: The inverse magnetostrictive effect provides a chance to detect the stress by measuring some magnetic parameters. So it is important to learn the effect of stress on some magnetic parameters. A measuring system to measure magnetic permeability and magnetic loss and a device to load uniaxial tension and pressure stress were developed. The result shows that magnetic permeability and magnetic loss increase with uniaxial tension stress increase and decreases with uniaxial pressure stress increase. It is also concluded that the relative change of magnetic permeability and magnetic loss decrease with increase of the included angle between the directions of the stress and magnetic field. These results suggest that magnetic permeability and magnetic loss can be further used to evaluate the stress in low-carbon steel.

Abstract: Two methods acquiring p-S-N curve for machine parts are given, namely directly searching out the p-S-N curve of the material from material database and using the idealized p-S-N curve. Reliability estimation methods of fatigue life of machine parts are derived under uniaxial constant amplitude load. Two kinds of circumstances (fixed stress and probabilistic stress) and two kinds of stress cycles (reversed cycle and unsymmetric reversed cycle) are considered. An iteration method is presented and the corresponding computer program is developed for estimating reliable life of machine parts. The engineering application results show that the calculated results are closer to experimental results. The suggested method can be convenient to fatigue reliability design of machine parts. It has good stimulative effect on popularization and application of existing anti-fatigue design method for machine parts, and high value of engineering application.

Abstract: Vehicle safety has increasingly become an economical factor for vehicle manufacturers and this has become most apparent in car safety [1-4]. Manufacturers are now spending considerable resources on safety research. Government requirements on safety have compelled manufacturers to carry out considerable number of crash tests to validate the safety of their cars [6-7]. The data from these tests is important in the development of simulation models employing finite element (FE) software. Many companies predict crashworthiness using commercially available software such as PAMCARSH and LS-DYNA. These simulations are based on mathematical constitutive equations and hence any simulation created is only as representative as the constitutive equations used. This project has studied the reliability of the material models used by LS-DYNA. Material models selected for analysis are used extensively by impact simulations software and were namely: Power Law Plasticity and Cowper/Symonds. Piecewise Linear Plasticity was also selected because it is based on a true stress/strain and is expected that the simulation would be representative. The models were developed using Belytschko-Lin-Tsay shell elements and were compared with experimental tests employing uni-axial tension strips carried out on three materials – aluminium, high strength steel and mild steel. The tests were carried out using a DARTEC tensile testing machine (up to strain rate of 2.0s-1) at UCE in Birmingham. Testing for the higher strain rates (aluminium up to 269.1s-1, mild steel up to 460s-1, and high strength steel up to 456.9s-1), were carried out at The Royal Military College, Shrivenham using a ROSAND tester.

Abstract: . In this paper, in order to determine whether the ballistic current enhancement saturates at very high stress level or can be further improved, the effect of uniaxial stress on the ballistic transport of the double-gated, ultrathin-body p-type silicon nanotransistor is investigated using a self-consistent device simulator, which combines the stress-dependent six-band k.p model and a semiclassical top-of-the-barrier ballistic transport model. Based on a semi-continuum atomistic lattice model, the size-dependent elastic constant correction has been for the first time coupled into this simulator. Our results presented here indicate uniaxial compressive stress at moderate levels improves ballistic performance by about 85% while uniaxial tensile stress slightly reduces ballistic drive current. Interestingly, higher compressively strained channel does not offer higher drive current. Although significant variations in the size-dependent elastic constants are found, the ballistic current shows only a small decrease after considering the elastic constant correction. Furthermore, the competition of injection velocity and carrier density related to hole effective masses is found to play a critical role in determining the performance of the nanotransistors.

Abstract: The orientational order generated in a cross-linked elastomer by uniaxial stress is probed with deuterium NMR spectroscopy. Spectra of technical unfilled natural rubber (NR) vulcanisates (cis-1,4-polyisoprene), locally swelled with o-dichlorobenzene-d4, exhibits quadrupolar doublets under elongation, which have an explicit dependence on the extension ratio and cross-link density. A new mechanical device was designed to fit into an NMR probe-head to permit the elongation of the networks in the interior of the magnet without removal of the sample thus avoiding the effect of the relaxation of the network chains after each step of uniaxial elongation and the observation of always the same section of the stretched sample. A molecular model of rubber elasticity was applied to describe the behavior of rubber network in mechanical and NMR experiments.